Studies in Prairie and Woodland 47 



significant permanent extension is concerned, by the increasing 

 severity of natural environmental conditions as we move west- 

 ward away from the woodland types of southeastern Nebraska. 



4. The high saturation deficit and the low soil moisture content 

 (often reaching the non-available point) of the prairie sites in 

 eastern Nebraska constitute barriers over which forest trees can 

 scarcely pass. We probably have herein the most ready explana- 

 tion as to why our natural Nebraska woodlands are confined to 

 the moist slopes of rather narrow valleys, and also the most prob- 

 able answer to the oft-repeated question as to the treelessness of 

 the prairies in general. 



5. The common forest types or communities of the region about 

 Peru in the order of their place in succession are as follows, be- 

 ginning with the most mesophytic: The linden-ironwood type, 

 the red oak type, the black oak-hickory type, the bur oak-yellow 

 oak type. A bur oak-yellow oak -black oak combination is also 

 quite common. The common forest type near Lincoln is the bur 

 oak-hickory type, often mixed with elm and black walnut. 



53 



